Kicking Up Dust

Much of the dust that blows into snowy areas—whether in the Rocky Mountains, the Himalayas, or the Hindu Kush—comes from deserts. Humans can’t dictate the location of deserts, but human activity does influence the amount of dust that blows out of them.

Between 1800 and 1880, Americans were penetrating deeper into the interior of continental United States, particularly in the Plains, the Rockies, and the Southwest. Human settlement brought building, farming, and grazing cattle and sheep—all of which disturbed the ground surface. The effects were especially pronounced in arid places.

“Disturbance matters. Parts of deserts that have never been disturbed blow almost no dust because whatever loose material was there blew away a long time ago,” Painter notes. “Left behind were biological and physical crusts that prevent emission of the loose material that might lie below.” In fact, undisturbed dry places lose very little dust, even during decades-long droughts like those that occurred during the Medieval Warm Period.

Lasting more than 50 years apiece, several deep droughts occurred on the Colorado Plateau from 760 to 1250 AD. Despite the intensity, desert pavement and cryptobiotic soils limited dust generation. (Graph derived from data published in Meko et al., 2007.)

Paleoclimate records suggest that there were several 30- to 50-year droughts in the American Southwest from 760 to 1250 AD, but dust emissions did not increase because desert pavements remained intact. Starting in the mid-19th century, significant cattle and sheep grazing began out West. It’s probably not an accident that snow cover began shrinking around the same time, though scientists still have not proven the connection.

Human activity has disturbed the deserts well beyond North America. The Himalayas get regular dustings from the Thar Desert along the India-Pakistan border, which witnessed an expansion of human activity in the 1800s. Further north, the Soviet Union diverted water from the Aral Sea, and now it’s a huge dust producer affecting the Tien Shan mountain range. Land practices over the past 30 years in Afghanistan have made that land a tremendous dust producer, as well.

Dust deposition has even affected the Antarctic Peninsula. “There was a doubling of dust deposition there since 1935,” Painter adds, “and it coincided with when sheep were introduced to Patagonia.”

All over the world, human activity has kicked up dust and left the landscape more vulnerable to the effects of drought. It has also sent dust across oceans, to places far removed from the source. It makes Painter wonder: “What are we going to do if we have a 30- to 50-year drought now?”